Field
The present specification generally relates to the manufacture of thin substrates with formed holes and, more specifically, to methods for laser drilling thin substrates using a sacrificial cover layer, and a work piece used to form holes in a substrate and a sacrificial cover layer.
Technical Background
Holes may be formed in glass articles by methods such as laser machining, photo machining, direct molding, electrical discharge machining, and plasma/reactive etching. Such glass articles may be used in a number of electrical devices such as interposers that route electrical signals between silicon microchips and organic substrates. Further, the glass articles may be used in life science applications, such as in digital polymerase chain reaction (dPCR) instruments.
In the laser drilling method, pulses of a UV laser are directed to a glass article in predetermined positions to thereby form holes in the glass article at the predetermined positions. The number of pulses applied at each predetermined positioned may be determined based on the desired depth of the hole in the glass article. The diameters of the holes formed by laser drilling may be modified using an optional etching process. In the etching process, an etching solution is applied to the surface of the glass article, such as by spraying or immersion, after the holes have been drilled into the glass article by the laser. The duration of exposure, temperature, concentration, and chemistry of the etching solution may be determined based upon the desired diameters of the holes in the glass article.
Laser drilling holes directly into a glass article may cause defects, such as micro-cracks or “checks,” at the entrance hole where the laser is incident on the glass article. Optimizing the laser exposure conditions, such as beam quality, beam focus, pulse rate, and pulse energy can reduce the number of defects in the entrance holes. However, currently available methods are not able to produce small-diameter holes with an acceptably low amount of defects, particularly when small-diameter holes are spaced relatively far apart. In this situation, the entrance holes may crack more easily, and even the slightest irregularity in roundness may be magnified during etching leading to a glass article with holes that have unacceptable roundness.
Accordingly, a need exists for alternative methods for forming holes in glass articles, such as thin glass, that do not result in cracking at the entrance holes where the laser is incident on the glass article.